The use of substrate integrated waveguide (SIW) circuitry for RF signal transmission can offer a planar, low profile alternative to traditional bulky, metallic waveguides and can be more efficient than two-wire cable or coaxial cable solutions in some applications. With SIW, relatively low-loss and high-Q waveguide structures can be realized as highly integrated planar microwave structures with compact size, at low cost, and with low interference due to the shielded environment.
It is possible to propagate several modes of electromagnetic (EM) waves within a waveguide. The physical dimensions of a waveguide determine the cutoff frequency for each mode. If the frequency of the impressed RF signal is above the cutoff frequency for a given mode, the electromagnetic energy can be transmitted through the guide for that particular mode with minimal attenuation. Otherwise the electromagnetic energy with a frequency below cutoff for that particular mode will be attenuated to a negligible value in a relatively short distance. The dominant mode in a particular waveguide is the mode having the lowest cutoff frequency. For a rectangular SIW this is the TE10 mode. The TE (transverse electric) signifies that all electric fields are transverse to the direction of propagation and that no longitudinal electric field is present. In some applications, a SIW structure that facilitates conversion from one EM wave mode to a different EM wave mode could be useful.